Various types of force sensors have been used to control motions of robots and industrial machines. Also, a downsized force sensor has been incorporated as a man-machine interface of an input device for electronics. In order to reduce dimensions and cost, a force sensor to be used in the above-described applications is required to be as simple as possible in structure and also to independently detect force for each coordinate axis in a three-dimensional space.
In view of the above description, at present, a generally used multi-axis force sensor has adopted a basic structure body which includes, as a mechanical structure portion, a force receiving body which receives force to be detected, a supporting body which supports the force receiving body, and a deformation body which is installed between the force receiving body and the supporting body to yield elastic deformation. Any desired force sensor can be constituted by adding to the basic structure body a detection element which electrically detects a deformed state of the deformation body and a detection circuit which outputs electric signals that indicate force in the direction of a predetermined coordinate axis and moment around a predetermined coordinate axis which have been exerted on the force receiving body on the basis of the obtained detection results.
As the detection element which detects a deformed state of the deformation body, there are used an element which takes out a mechanical strain occurring at a specific site of the deformation body as an electric signal and an element which takes out displacement occurring at a specific site of the deformation body as an electric signal. A representative detection element which is of a strain detection type of the former is a strain gauge which is attached to a specific site of a deformation body in which a mechanical strain resulting from exerted force is electrically detected as change in electrical resistance of the strain gauge. On the other hand, a representative detection element which is of a displacement detection type in the latter is a capacitive element which is constituted with a displacement electrode fixed at a specific site of a deformation body and a fixed electrode fixed at a part opposite to a supporting body. When displacement occurs on the deformation body upon exerted force, a distance between the displacement electrode and the fixed electrode is changed, by which the displacement is electrically detected as change in capacitance value of the capacitive element.
For example, in Patent Documents 1 and 2 given below, as a deformation body which connects between a force receiving body and a supporting body, there is disclosed a force sensor in which a plurality of columnar members and a plurality of diaphragms are used. Each of the columnar members is such that an upper end thereof is fixed to the force receiving body via a diaphragm and a lower end thereof is fixed to the supporting body via a diaphragm. Therefore, when force is exerted on the force receiving body in a state that the supporting body is fixed, each of the columnar members undergoes displacement due to elastic deformation of the diaphragm. A displaced state thereof is detected by using a capacitive element, thus making it possible to detect force in the direction of each coordinate axis and moment around each coordinate axis in an XYZ three-dimensional orthogonal coordinate system. Further, Patent Documents 3 given below discloses a variation of the force sensor disclosed in Patent Documents 1 and 2, which is a force sensor that uses, as a deformation body, a group of pairs of columnar members, each of which is arranged in an inclined manner so as to form a V-letter shape.